Preheat your oven to 375°F (190°C).
Bring a large pot of salted water to a boil and cook the jumbo shells according to package directions until al dente, then drain and set aside.
In a non-stick skillet over medium heat, cook the ground turkey until browned and crumbled, about 5-7 minutes.
Add the fresh baby spinach to the skillet with the turkey and sauté until completely wilted, then remove from heat to cool slightly.
In a medium mixing bowl, combine the ricotta cheese, egg white, parmesan, garlic powder, oregano, sea salt, and black pepper.
Stir the turkey and spinach mixture into the ricotta mixture until well combined.
Spread half of the marinara sauce into the bottom of a small baking dish.
Stuff each cooked shell generously with the turkey and ricotta mixture and place them in the baking dish.
Top the shells with the remaining marinara sauce and sprinkle with the mozzarella cheese.
Cover with foil and bake for 15 minutes, then remove the foil and bake for an additional 5 minutes until the cheese is melted and bubbly.